D-Link DGS-6600-48TS Configuration Guide - Page 272

Volume 4-Layer 3 Configurations / Chapter 28-Open Shortest Path First Version 3 (OSPFv3) Chapter Overview When going from IPv4 to IPv6, the basic OSPF mechanisms remain unchanged from those documented in OSPFV2. Both IPv6 and IPv4 have a link-state database composed of LSAs and synchronized between adjacent routers. Initial synchronization is performed through the Database Exchange process, which includes the exchange of Database Description, Link State Request, and Link State Update packets. Thereafter, database synchronization is maintained via flooding, utilizing Link State Update and Link State Acknowledgment packets. Both IPv6 and IPv4 use OSPF Hello packets to discover and maintain neighbor relationships, as well as to elect Designated Routers and Backup Designated Routers on broadcast and NBMA links. The decision as to which neighbor relationships become adjacencies, and the basic ideas behind inter-area routing, importing external information in AS-external-LSAs, and the various routing calculations are also the same. The major OSPF data structures are the same for both IPv4 and IPv6: areas, interfaces, neighbors, the link-state database, and the routing table. All LSAs with known LS type and AS flooding scope appear in the top-level data structure, instead of belonging to a specific area or link. AS-external-LSAs are the only LSAs defined by this specification that have AS flooding scope. LSAs with unknown LS type, U-bit set to 1, and AS flooding scope also appear in the top-level data structure. 1.The Area Data Structure Area specific configurations are stored in the area descriptor. There are many parameters that are mostly used by the OSPFv3 protocol manager. The first stores the per area LS database. The second is a list of all active neighbors from the RIB. The OSPFv3 protocol tells the RIB when neighbors are created, deleted, or when their state changes. On the other hand active is only used by the OSPF protocol manager. Active tracks the number of neighbors which are in state FULL. If the number is zero the area is considered inactive. This counter is used to determine if a router is an area border router. 2.The Interface Data Structure Every configured interface is represented by a struct iface. It stores values like the link state, baudrate, MTU, and interface type. There are some additional OSPFv3 specific parameters like the interface metric and interface state. Three neighbor pointers are pointers to the active DR or BDR neighbor or NULL if there is none. An interface can have up to three concurrent timers running and therefore three different event structures are needed. 3.The Neighbor Data Structure Struct neighbor represents the neighbor relationship from the local point of view. To maintain a session successfully a LS retransmission and request list is required plus a list for the database. A few values are only used in the EXCHANGE phase when Database Description packets are transmitted. The interface, over which this neighbor is reached, is stored in iface. The neighbor structure is per interface so if two routers are connected via two different networks two different neighbor structures will be created for the same router but the structures are added to different interfaces. DGS-6600 Configuration Guide 272